If we heat any gas, will it emit photons? If we heat up any gas (let’s say hydrogen), will it emit photons? And does this mean, if we freeze it, it absorbs photons, am i right?
 A: Short answer: Yes. All matter emits light when heated because of incandescence, but they do not absorb light when cooled.  
Everything that has any heat in it emits light if it is above absolute zero, and the wavelength of this light is inversely proportional to its heat. This is the reason why we can see body heat on infrared cameras. Our bodies are just the right temperature to emit infrared light that has too long of wavelengths for us to see with our own eyes but can be picked up by cameras. All forms of matter emit light, but when heated hot enough, it will emit light with just the right amount to be seen by us. This is why a burning stove or molten metal will glow red. Because it has just the right temperature to emit red light (which is the lowest wavelength of visible light and therefore the lowest temperature to emit visible light.). Theoretically though, if something is heated enough, it can emit any wavelength of light including green, blue, and even purple though it would take about 71,000 degrees Fahrenheit for something to glow purple.  
For gasses, the same thing is true. This can be seen in videos of people farting on infrared cameras. The reason it is hard to see gas glow is that the hotter the gas gets, the less dense it becomes, and so a buoyant force is acted upon it and it quickly mixes with cooler air.  
As for if something cold doesn't absorb light, no it doesn't absorb light any more than a material that is warmer. Technically everything absorbs light when its hit by photons, but the temperature does not affect that. The reason for that is that Celcius and Fahrenheit are not absolute. Only Kelvin is absolute. For example, something that is -20c is 253.15K. No matter how many degrees below zero something gets in Celcius, it will always yield a positive temperature in Kelvin. That is because you can't have negative heat. Everything above absolute zero has some amount of heat, and because it has heat, instead of absorbing light, it emits light of a lower wavelength.
My name is Erik Low, and thank you for coming to my Ted Talk. :)
